As shown in FIG. 1, structure of a prior art DMOS (Double-diffusion Metal Oxide Semiconductor) product are shown. The DMOS product includes a substrate 1, a dielectric 2, a metal 3, and a passivation layer 4. Wherein, the passivation layer 4 is a silicon nitride layer with a thickness about 10000 angstroms.
Generally, a high voltage DMOS product is required to undergo a HTRB (High Temperature Reverse Bias) test and HTGB (High Temperature Gate Bias) test. The DMOS product needs to meet different requirements according to different applications. Some low-end products merely need to pass a 168 hours test, but some high-end products are required to pass a 1000 hours test. It can be found that in actual production, when many products undergo a test of more than 500 hours, a large amount of aluminum is corroded after the product being soaked in a hydrochloric acid (i.e. pinhole test), and the passivation layer 4 has cracks thereon, such that an electric leakage can easily occurs.